Why i can't answer on here now for The minimum length of an answer is 15 characters ?

Just add periods or dashes.

You have to type 15 characters. It's not hard.

I am guessing they are hoping for a better answer than just "yes", "no"

Use the space bar....You  can still give yes or no answers.

When someone has no points and need to ask a question, the fastest way to get those points is to answer in the polls section with yes/no answers. Yahoo thinks it’s a cheap way to get points so it’s forcing people to answer with at least 15 characters but of course, people will find a way around this so they put yes/no followed by a bunch of periods. 

Now it’s kind of pointless since yahoo isn’t subtracting points for asking questions. 

You can Answer you just need to make it 15 Characters at Least you cant do Short Answers anymore